1. Field of the Invention (Technical Field)
The present invention relates generally to methods and apparatuses for in situ remediation of organic products, such as hydrocarbons, and inorganic products, such as metals, from subsurface soil and groundwater. In situ remediation of excavated materials also may be conducted by the present invention.
2. Background Art
The remediation of contaminated soil and groundwater has become an international priority. Subsurface soil and groundwater are contaminated with organic and inorganic products in a number of ways.
Contamination by petroleum products, including gasoline, diesel fuel, and heating oil, is an ubiquitous problem, particularly by leakage from underground storage tanks. In addition, spills and improper disposal of petroleum products cause many contaminated sites.
The Federal Agency in charge of clean-up of underground storage tank spills, which regulates only a portion of the hydrocarbon spills in the United States, has estimated that there are a minimum of 400,000 leaking tanks. A relatively low figure for average costs of clean-up of an underground storage tank leak is approximately $200,000. Remediation technology is of significant importance to the taxpayers of the nation as well as industry.
In addition to petroleum products, contamination by other organic products occurs at numerous contaminated sites. Examples of such other organic contaminants are halogenated hydrocarbons, such as trichloroethylene (TCE), carbon tetrachloride, and methylene chloride, which have been used for many years as degreasers in various industries. Alcohols, ketones, esters, aromatics, olefins, alkanes and other organic compounds and families of compounds are also widely used in industry and consequently contaminate various sites. The present invention is capable of remediation of any hydrocarbon product which may be bioremediated. Such hydrocarbon products consist of the majority of natural and man-made organic materials.
The major remediation technologies applied to in situ hydrocarbon contamination earlier in the history of such remediation were extraction, that is excavation of contaminated soil, and a technology known as "pump and treat." "Pump and treat" technology consists of pumping water out from underground and treating it above ground. A third major technology, used later in the history of remediation, is vacuum extraction. These technologies were not particularly successful and were extremely expensive. The technology of excavation is now being phased out by regulatory action in most states because it simply consisted of digging up contamination and placing it elsewhere. On occasion, excavation was followed by remediation above ground on the site or in a particular remediation facility. This approach is still being used and is useful. In fact, the present invention has the capability of providing the remediation above ground for such excavations or at a regional, above ground, encapsulated treatment facility. However, excavations are also extremely expensive and quite often can not reach deep enough to totally remediate the site. Furthermore, excavations often endanger surface structures due to weakening of the subsurface below them. Therefore, the percentage of contaminated sites which can in fact be remediated by excavation is fairly small, on the order of 10% to 15%.
With respect to "pump and treat" technology, it has been and continues to be the most often applied technology. However, practitioners in the art have determined that "pump and treat" technology is inefficacious. It often extends to tens or hundreds of years to reach statutory clean-up requirements. Because overall project costs are related to the length of the project, "pump and treat" technology is often virtually the most expensive technology which could be applied.
The third alternative, vacuum extraction of soil contamination, is being applied more consistently throughout the country at the present time. It has a higher rate of success, probably on the order of forty to sixty percent, if the criteria is removal of the contamination down to statutory levels Vacuum extraction would be exceedingly successful if the only concern was subsurface vapors. However, this is not the only concern with respect to remediation of a site. As currently used by most practitioners, vacuum extraction technology is a high volume extraction. The present invention uses a low volume approach for the purpose of allowing bioremediation and for the purpose of controlling the amount of contaminants passed out to the atmosphere as stack or vent gases. High volume vacuum extraction exceeds air quality standards and thus requires expensive air treatment. The air treatment is often as costly as the original remediation itself. The reason that soil vacuum extraction fails to completely remediate the majority of sites is the fact that it is dependent for its physical success on the diffusion rate of volatile compounds from within the liquid contamination to the interface with the vapor phase. This diffusion is extremely slow. This means that one consistently gets a vent gas emission curve that is very high for a few months and then drops rapidly to an extremely low remediation rate. Again, we see the effects of time and concomitant increased total cost. Pure soil vacuum extraction technology is a long-term process if one wishes to remove the residual, liquid contamination by waiting for it to diffuse volatiles to the vapor phase. Secondly, this technology tends to fail if the contamination is not made up entirely of highly volatile compounds because that is all the vacuum addresses. An example of a low volatile compound that is difficult to remediate by pure vacuum extraction is diesel fuel. Thirdly, vacuum extraction only occurs above the water table and thus has a strong tendency to fail to clean contaminated ground water.
A further technology, air stripping of contaminated water at the surface of the ground, is a long practiced art. It depends on a high air-to-water ratio and is controlled by the rate of movement of the contaminant from the water phase into the vapor phase, whereupon the contaminant is exhausted to the air.
A fifth technology, bioremediation, is a theoretically successful technology but is failing in general because of the problems of high costs and difficult physical delivery of the components that would support the bioremediation.
The present invention overcomes the limitations expressed above of the prior technology. The invention employs the advantageous activities of vacuum and of air stripping and combines them with the theoretically valuable remediation technology known as bioremediation. In essence, the invention provides an integrated system capable of delivering the necessary chemical and physical components of a remediation technology to the various parts of contamination underground in ratios that allow maximum remediation stress on the contamination. Unlike with the prior art, remediation stress is variable throughout the plumes of contamination to address the plumes' changing characteristics.
Inorganic products, such as iron, manganese, chromium, selenium, and nitrates, cause contamination problems as well. Common and dangerous inorganics are spilled by industry, requiring clean-up of the underlying soil and groundwater. Inorganic compounds such as discussed above are highly receptive to precisely the same design and installation characteristics of the present invention discussed for hydrocarbon remediation above.
The majority of heavy metals such as iron, manganese, nickel, cobalt and chromium are all precipitated into insoluble oxides and hydroxides at a high oxygen content of groundwater. This is otherwise known as a high redox potential. The high redox potential in contaminated groundwater is achieved by the air injection portion of the current invention. In addition, the precipitation of metals by the activity of microbes is a well known phenomena. This is often used in mining by microbiological processes. In this case, the microbes are unlikely to be common soil microbes and therefore non-indigenous microbes must often be used.
Nitrate contamination in groundwater is of serious concern because of health problems associated with this compound. Nitrate remediation can be accomplished through the exact same physical system for hydrocarbons. However, the chemical processes are reversed. Instead of adding oxygen to cause oxidation, what is necessary is to add a hydrocarbon or naturally occurring organic as a food source to microbes and encourage them to make use of the oxygen in the nitrate compound. In this case, a gas develops, nitrogen, whose release from the site is controlled by the vacuum of the system.
The United States and other countries need effective and economic methods for the in situ removal of such organic and inorganic contaminants in order to avoid the extraordinarily high cost, effort, and the time required to excavate and either replace or decontaminate contaminated soil sites, as well as to employ other existing methods. The prior art does not present efficient and effective methods.
For example, U.S. Pat. No. 4,730,672, to Payne, discloses a closed-loop process for removing volatile contaminants. Payne deals strictly with volatile contaminants whereas, in fact, the majority of hydrocarbon contamination sites are made up of non-volatile constituents. It is these non-volatile constituents which must be attacked by bioremediation. This statement is particularly true if the contamination occurred several years before bioremediation, which is faced in the majority of sites across the United States. In Payne, a withdrawal well is surrounded by multiple injection wells. Pressurized air is injected into the ground water through the injection wells, and is withdrawn under vacuum from the withdrawal well. The output of the withdrawal well is connected to the input of the injection wells through a series of scrubbers, condensers, and neutralizers which remove contaminants from the air stream. The recycling of air through the system increases the likelihood of contaminating the groundwater through the injection wells. The process of recycling, as portrayed in Payne, provides only for volatiles and not non-volatiles, which are more abundant, and is unacceptable by regulatory agencies in the majority of states.
U.S. Pat. No. 4,765,902, to Ely, et al., discloses a process for remediation of hydrocarbon contaminants in soil. A borehole is extended down to a water table beneath a contaminated vadose zone. This borehole is then evacuated in a controlled manner so as to draw air through the vadose zone, causing hydrocarbon contaminants in the vadose zone to be volatilized and drawn up the borehole. The present invention is an integrated system and is not restricted to partial remediation of the site as is the process of Ely. The patent of Ely provides for removal of volatiles only.
U.S. Pat. No. 4,745,850, to Bastian, et al., discloses a wind-driven, self-ventilating system for extracting volatile organics from soil. A wind-driven turbine is positioned over a well bore. The well bore extends downwardly to a bore or conduit which extends generally horizontally through a contaminated soil zone, and which is connected to one or more air intake boreholes. The wind-driven turbine draws air through the boreholes and the horizontal conduit, thereby drawing volatile contaminants from the surrounding soil. This patent, therefore, discusses a process which in fact addresses only the minor parts of the needed remediation process. It is essentially a soil vacuum technique and therefore fails in a majority of cases to totally remediate the soil residual and to effectively remediate contaminated groundwater. This process is what is called in the industry a passive soil venting technique. It has a very high failure rate because it does not evacuate sufficiently and strenuously and deals only with vapor contamination and not other types of contamination. Passive soil venting systems are not acceptable to the majority of state regulatory agencies. Bastian does not provide for remediation of ground water, free-product, or of non-volatile components.
U.S. Pat. No. 4,588,506, to Raymond et al., discloses the injection of a dilute solution of hydrogen peroxide into a contaminated soil formation for the purpose of stimulating the biodegradation of organic contaminants in the soil. The process is supplemented by the intermittent spiking of the hydrogen peroxide concentration, after biodegradation is complete in a selected area, for the purpose of killing and thereby removing the biota in the selected area and thereby increasing the permeability of the soil. The process discussed in this patent is the addition of oxygen in the form of hydrogen peroxide to groundwater. It has the advantages of stimulating biodegradation. It has seldom been successful because of the difficulty of delivery of the oxygen throughout the system. This patent depends on hydrologic management of the subsurface which is a very complicated and difficult process that is similar to the difficulties that are experienced in "pump and treat." The few times this process has been successful has generally been so at exorbitant costs. For example, one site was cleaned to standards in California by the use of hydrogen peroxide. The hydrogen peroxide costs alone, not including all the hydrologic manipulation costs, was over $400,000. Hydrogen peroxide is an expensive chemical in large volumes. It is also an explosive chemical and this increases risks and costs at the site. A much less costly and more controllable use of oxygen is by air injection, as with the present invention. Raymond does not provide for remediation of free-product, vapors, or soil residual.
U.S. Pat. No. 4,401,569, to Jhaveri, et al., discloses a process of removing contaminated groundwater from a soil formation, treating it with nutrients and microorganisms to cause biodegradation of the contaminants, and returning the treated water to the soil formation. The treated water also contains nutrients and microorganisms, thereby further facilitating in situ decontamination of water in the formation. This method is expensive in that it requires removal and reinjection of water. This process of the Jhaveri patent is essentially a "pump and treat" process. It therefore fails from the standpoint of all "pump and treat" systems and has a very low probability of success and a very slow rate of success, as discussed above. Further, indigenous microorganisms are not controlled and used as they are in the process proposed herein. Injection of non-indigenous microorganisms is not acceptable to the majority of state regulatory agencies. The injection of combined nutrients and microorganisms quite often yields a biologic bloom around the well which decreases permeability and decreases or causes a cessation of the process. The present invention does not inject nutrients through the air injection wells for this very reason and allows the other nutrients in the groundwater and in the soil moisture to control the rate of the process. This avoids costly failures caused by biologic bloom around the injection well. Jhaveri does not provide for treatment of vapors, free-product, or soil residual.
U.S. Pat. No. 3,846,290, to Raymond, discloses a process for reclamation of groundwater contaminated with hydrocarbons. In accordance with the method of this patent, nutrients and oxygen are injected into a contaminated subsurface groundwater aquifer through an injection well located near a producing well. The nutrients and oxygen stimulate naturally occurring microorganisms in the water to consume hydrocarbon contaminants. Additionally, the injection of nutrient-bearing water into the aquifer causes a flow of water from the injection well to the producing well, whereby the producing well continuously draws decontaminated water from the aquifer. Although the method of the Raymond patent is intended to purify water in a subsurface aquifer for subsequent production it does not remove contaminants in the overlying vadose zone, nor does it disclose use of injected microorganisms, nor does it remediate vapors, free-product, or soil residual.
U.S. Pat. No. 3,665,716, to Rogers, discloses the removal of noxious gases from an underground refuse disposal cavity. The extracted air is conveyed to a purification facility where it is purified and then released to the atmosphere. This method is not directed to removal of contaminants from the soil surrounding the cavity or from groundwater. Rogers relates only to vacuum extraction techniques which have been discussed above.
U.S. Pat. No. 4,435,292, to Kirk, et al., discloses a method for injecting flushing fluid into a contaminated zone, collecting the liquid after flushing through the zone, and treating the liquid to extract contaminants. The system is closed in that the flushing fluid is repeatedly reinjected into the contaminated zone. The Kirk patent is in fact a "pump and treat" technology and suffers from all of the problems associated with hydrologic management in the "pump and treat" technology, which has failed to provide cost effective and rapid clean-up in most cases. In many states, regulations require very expensive treatment of water reinjected or discharged. The current invention avoids this cost entirely. Kirk does not address free-product, soil residuals, or vapor contaminants.
U.S. Pat. No. 4,183,407, to Knopik, U.S. Pat. No. 4,842,448, to Koerner, et al., and U.S. Pat. No. 4,593,760, to Visser, et al., disclose methods of extracting volatile contaminants from a vadose zone by vacuum pumping. The method of Koerner comprises sealing the surface surrounding an extraction pump intake. Knopik employs horizontal collection shafts. Visser requires the use of various fill materials in the extraction well. The patents of Knopik, Koerner, and Visser disclose pure vacuum extraction. This technology has been discussed above and has a high failure rate with respect to removal of all forms of underground contamination. In addition, the current invention involves vacuum for the purpose of controlling vapors that are generated by the rest of the remediation system and not solely for the purpose of vacuum extraction of volatiles.
U.S. Pat. No. 4,832,122, to Corey, et al., discloses a method for in situ remediation of groundwater contaminated by volatile contaminants by pumping fluid via a first pump to an area beneath the water table, the fluid filtering up through the contaminated zone and being pumped out from above the contaminated zone by a second pump. The method employs horizontal distribution and collection shafts. The method of Corey involves vacuum extraction above the water table and air injection below the water table in a design around the contamination. Such a technology will contain most of the contamination on most sites and not allow it to migrate further. However, this technology will not allow remediation of the contamination itself. Therefore, the method of Corey depends on allowing natural degradation to remediate the contamination. This process takes on the order of decades because of the loss of oxygen within the contamination itself, thus reducing biological activity. Furthermore, Corey addresses the remediation of the volatile portion of contamination only. As discussed above, this is the minor portion of most hydrocarbon contamination sites.
U.S. Pat. No. 4,249,605, to Slater, et al., discloses a method of separating oil and water within oil wells by application of heat provided by a solar furnace. The system requires injection of water below the surface. In many states this is either forbidden or heavily regulated with subsequent heavy costs on the remediation technology of the site. The current invention uses heat for biological stimulation and is not concerned with the process of separating oil and water by the use of heat.
U.S. Pat. No. 4,289,204, to Stewart, et al., discloses a method of treatment of crude oil, well fluids, and well equipment via a solar heater. The heat helps demulsify and remove paraffin from an oil well. Stewart applies heat in the form of solar heat for the purpose of breaking down paraffins and causing them to flow more readily and become collectable in an oil well. The present invention does not use heat for the breakdown of organic constituents. Paraffins which are present in hydrocarbon contamination are removed in the current invention through the effects of bioremediation.
U.S. Pat. No. 4,850,745, to Hater, et al., discloses a method for bioremediation of petroleum-contaminated soil adjacent to an excavated cavity by provision of microbes, air and nutrients. Microorganisms are provided in dry form to the bottom of the excavated cavity then covered with gravel, a nutrient-providing pipeline, and further dirt and gravel. Hater has the advantage of using bioremediation at the site. However, it requires excavation prior to its application. The problems with excavation have been discussed above. They include excessive costs unless the contamination is quite small and quite shallow, the lack of acceptance of most regulatory state agencies of placing the contaminated excavated soil in landfills, the need to treat the excavated soil above the surface which increases project costs, and the restriction of excavation to those areas that do not entail potential structural damage due to the excavation. The net result of these constraints on excavation causes excavation to be a minor remediation technology throughout most of the United States. Therefore, the Hater method is severely restricted in its actual applicability, which is not the case with respect to the current invention. Furthermore, the Hater patent does not deal with ground water contamination because of the difficulty of excavation below the water table. Furthermore, Hater is limited in space and time by the travel velocity of the microbial population. This has been estimated to be on the order of from five to ten feet per year, except under very unusual circumstances. Therefore, the method proposed in Hater will not totally remediate a site unless contamination is located very close to the excavation. One must add the necessity for additional introduction by such a method as the present invention at distances greater than approximately twenty feet away from the excavation. The reason for this is twofold: acceleration of the remediation to reduce total project costs and the introduction of air passively through the sidewall of an excavation depends entirely on the flow rate of the groundwater system to carry oxygen downgradient. Groundwater systems are notoriously slow and removal of oxygen occurs along that flow path. Therefore, oxygen does not reach far from such an excavation.
U.S. Pat. No. 4,323,122, to Knopik, and U.S. Pat. Nos. 4,241,787 and 4,296,810, to Price, disclose methods for extracting organic liquid from groundwater by filtration of the organic liquid through a hydrophobic liquid permeable membrane. The organic liquid is pumped to the surface for disposal while the permeable membrane remains exposed to the water/organic liquid mixture. The problems with these and similar methods are that, while pumping increases the rate of extraction, pumping places stress on the permeable membrane, which rapidly breaks down, and produces extracted liquid contaminated by water. The extracted liquid must then be disposed of as hazardous waste or further treated to remove the water before the hydrocarbon product may be refined. This technology is known as "skimmer" pumps. Inasmuch as these need to be of reasonable size to be effective, the wells in which they are placed must be greatly oversized compared to the wells used in the present invention. The net result is a very expensive well system, and consequently few of these wells are emplaced on a remediation site. This fact means that they must be capable of extracting the free-product from a long distance. Additionally, the process produces water which must be pumped, treated and then disposed of at a per gallon disposal cost. This generates the need for a permit from the Environmental Protection Agency (EPA) which creates costs of about $2,000 per week simply for analyzing the disposed-of water. Additionally, high maintenance costs are incurred to keep the system from biofouling. The present invention does not use a free-product filter connected to any free-floating pumping facility and thus avoids biofouling. Secondly, the present invention operates in as small a well as one desires. The free-product filter of the present invention can be emplaced within the normal air-insertion wells of the present invention.
U.S. Pat. No. 4,872,994, to Jakob, discloses a method for separating gasoline from water within a water well by means of a floating, hydrophobic wick, the gasoline descending by gravity from the wick to a storage vessel for later extraction. The present invention does not employ such a wick.
U.S. Pat. No. 2,523,091, to Bruce, discloses an apparatus for separating oil from water within a well and separately extracting the two fluids. The apparatus does not permit extraction only of oil. The technology proposed by Bruce does not result in a contaminant free water. For this reason, water must also be treated on site as a hazardous waste thus vastly increasing the cost of the remediation technology. On the other hand, the technology proposed in this application leaves water in place for remediation. The present invention sends the free oil or gasoline or diesel to the surface in an approximately 98% pure product, thus allowing its transportation to refineries and not causing it to be treated as a hazardous waste with consequent costs.
U.S. Pat. No. 4,126,556, to Swanson, et al., discloses a method for separating immiscible liquids by siphoning. The method does not permit extraction of liquid mixed or partially mixed with water. The present invention does not use siphoning in any manner. It does remove an essentially pure organic liquid and leave the contaminated water in place for treatment. It thus does not require water treatment under hazardous waste conditions at the surface of the site and avoids the excessive costs of doing so.
U.S. Pat. No. 4,806,148, to Ottengraf, U.S. Pat. No. 3,216,905, to Baptist, U.S. Pat. No. 3,828,525, to Copa, et al., U.S. Pat. No. 4,662,900 to ottengzaf, and U.S. Pat. No. 4,723,9688, to Schippert, et al., disclose methods or apparatuses for purifying contaminated air by biological means and a semi-solid material such as compost or sludge which is termed a substrate. None disclose a method for decontamination of air using microbe-impregnated water rather than a semi-solid filter bed, or substrate. The above patents all deal with the relative advantages of various solid substrates within bioreactors. However, microbes do not need this substrate. The substrate itself is a very expensive addition to the treatment of waste gases by microbes. The current invention makes no use of substrate.
Despite the teachings of the prior art, there has not been previously available a method for in situ removal of organic and inorganic contaminants from groundwater in a subsurface aquifer, while leaving the treated water in place, as well as removal of such contaminants from the surrounding soil or vadose zone. Nor has there been available an integrated method for extraction of free-floating contaminants on the water table synchronously with the additional decontamination of soil residual vapor and contaminated ground water. There has also not been previously available an integrated method for isolating, fermenting, and reinjecting indigenous, desirable microbes for decomposing and volatilizing underground contaminants, nor injection via use of the same installed physical system used for other decontamination activities at the site. Nor has a method existed whereby air filtered through a contaminated zone is decontaminated by passage through microbe-impregnated water at ground level. The present invention results in an integrated system maximizing the benefits of both previous and new technologies in a manner which achieves a cost effective and rapid remediation unable to be achieved by the individual application of any previous patents or non-patented techniques.
Hydrocarbon contamination occurs in four types of contaminant form: vapors; free-floating product in liquid form; soil residual in liquid to semi-liquid form; and dissolved groundwater contamination. Not all four phases necessarily occur at each remediation site. Floating free-product does not occur without attendant soil residual contamination extending outward from the free-product plume. Soil residual contamination can, but seldom does, occur by itself. Contaminant vapors do not occur by themselves. They require the attendant presence of at least one of the following: contaminated groundwater, soil residual, and/or free-floating product. Contaminated groundwater is not known to occur without the presence of at least soil residual contamination. The presence of free floating product guarantees the contamination of groundwater which often extends outward a considerable distance from the location of the free-product. A remediation technology which has the capability of attacking only one type of contamination will not totally remediate the site. Despite the teachings of the prior art there has not been previously available an inexpensive system which attacks all four of types of contamination synchronously. The present invention attacks all four types of contamination, if present, synchronously. It attacks the four types of contamination in such a manner that there is no significant increase in costs for attacking either one or all four types of contamination.
Contamination at a hydrocarbon remediation site can occur in three separate geological conditions. It can occur solely in the soil column above the capillary fringe. It can and usually does occur in the soil column and the capillary fringe and it can and usually does occur in the soil column, the underlying capillary fringe and the underlying groundwater body below the water table. Despite the teaching of the prior art there has not been previously available a method for simultaneous attack on all three geologic conditions in which contamination is found. The present invention synchronously attacks all three geologic conditions where necessary. It does so without a significant increase in cost for attacking solely one of the geologic conditions.
The remediation of free-product and thus removal of continuous contamination of the site is enhanced by the use of the present invention. This results in remediation speedup at the site. Despite teachings of the prior art there has not been previously available a method for coupling the pumping removal of free-product with the removal efficiency of an additional technique, thus speeding up the entire remediation of the site.
Despite the teachings of the prior art, there has not been a method of integrating the remediation stress of single remediation technologies into a remediation stress which can be varied in intensity and type of stress. Contamination characteristics vary over a site and change with time as remediation occurs. Thus, a successful remediation technology requires it be varied in intensity and type of attack throughout the contamination over time. The present invention permits this by valving and by the application of its inherent parts. For example, in an old contamination, from which the volatiles have gone, little remediation takes place by vacuum, but the residual can be cleaned by bioremediation.